More than two-thirds of teens aren’t getting enough sleep on school nights and that’s a problem. According to the latest study by the Centers for Disease Control and Prevention, sleepy teens were more likely to engage in risky health behaviors, compared with their 8-hours-a-night peers.

Last year, the medical journal Sleep published a series of studies on the consequences of sleeplessness among teens. I wrote, at the time:

Researchersfound that for each hour of lost sleep, levels of psychological distress rose by 5% in nearly 3,000 17-to-24-year-olds who were followed for 12 to 18 months. Overall, short sleepers were 14% more likely to report symptoms of psychological distress on a standard test, compared with people who got adequate sleep. The effect was especially pronounced among young people who already suffered from anxiety; in this group, lack of sleep triggered more serious mental health problems like full-blown depression and even bipolar disorder, according to the study’s lead author, Professor Nick Glozier. But even among those who began the study in good health, less than five hours of sleep meant tripling their odds of psychological distress.

The new findings, which were based on data from the 2007 National Youth Risk Behavior Survey, fit in with past research. The study authors found that 69% of more than 12,100 adolescents aged 12 to 18 reported getting less than the recommended 8 hours of sleep on the average school night. Sleep-deprived kids were more likely than their well-rested peers to report the following 10 risky health behaviors:

Drank full-sugar soda at least once per day

Participated in 60 mins. of physical activity fewer than twice in the preceding week

Spent three or more hours each day on the computer

Had been in at least one physical fight

Smoked cigarettes

Drank alcohol

Used marijuana

Was sexually active

Had feelings of sadness or hopelessness

Seriously considered attempting suicide

Of course, it’s impossible to know whether teens’ sleeplessness contributed to these problems, or the other way around. It’s could well be that things like depression, lack of exercise, Internet use and drinking high-sugar beverages may interfere with proper sleep. But the study, which was published online by Preventive Medicine, is the first to draw associations between lack of sleep and risky health behaviors on a national scale.

The researchers suggest that public health policies encouraging more sleep in teenagers — such as starting the school day later —are needed. “Many adolescents are not getting the recommended hours of sleep they need on school nights. Insufficient sleep is associated with participation in a number of health-risk behaviors including substance use, physical fighting, and serious consideration of suicide attempt,” said the CDC’s Lela McKnight-Eily in a statement. “Public health intervention is greatly needed, and the consideration of delayed school start times may hold promise as one effective step in a comprehensive approach to address this problem.”

Meredith Melnick is a reporter at TIME. Find her on Twitter at @MeredithCM. You can also continue the discussion on TIME’sFacebook page and on Twitter at @TIME.